Frequency multiplier



E. G. LINDER FREQUENCY MULTIPLIER Filed March 27, 1941 June l1 Snventor Patented June 11, 1946 FREQUENCY MULTIPLIER Ernest G. Linder, Philadelphia, Pa., assgnor to Radio Corporation of America, a corporation of Delaware Application March 27, 1941, Serial No. 385,447

(Cl. Z50-36) 15 Claims.

This invention relates to frequency multipliers, and especially to ultra high frequency electronic devices in which the frequency of generated scillations is increased by compressing electronic pulses.

Ultra high frequency oscillations have been generated by directing electrons at high velocities through suitable apertures in a resonant cavity. The frequency of the generated oscillations is determined by the resonant characteristic of the cavity. The present invention provides means for increasing the frequency of oscillations by compressing, increasing the velocity of pulses 0f electrons, and directing the electrons through a resonant cavity or resonant circuit. While the multiplication of lfrequency by compression of pulses of electrons is the principal object of the invention, another object is to provide means for generating discontinuous wave trains of ultray high frequency energy. Another object is to provide means for generating pulses and increasing the frequency of the pulses by compression. Another object is to provide means for multiplying by any factor or continuously varying the frequency of an oscillatory current.

The invention will be described by referring to the accompanying drawing in which Figure 1 is a schematic diagram of one embodiment of the invention; Figure 2 is a graph illustrating a mode of operation; and Figure 3 is a schematic diagram of a modification of the invention.

Referring to Figure 1, within an evacuated envelope l are mounted at the endsof the envelope a cathode C and a target electrode T. Between the cathode and the target electrode the following elements are mounted in the order named: a space charge control grid GI, an accelerating grid G2, Velocity control grids G3, G4, a phasing grid G5, and a resonant cavity R. An output loop P is inserted Within the cavity R.

The control grid GI and cathode C are connected through a biasing battery 2 to an oscillator 3. The accelerating grid G2 is connected to a source 5 of positive potential. The control grids G3 and G4 are connected together and through a biasing battery 1 to a square Wave generator 9. The phasing grid G5 and resonant cavity R are connected together and through a biasing battery Il to the square wave generator 9. The terminals of the square wave generator are connected to a resistor i3 which is grounded between its terminals. The target electrode T is connected to the positive terminal of a battery I5 whose negative terminal is grounded. The

envelope is provided with magnetic focusing means, which may be a solenoid I1, energized by a battery I9.

The mode of operation is as follows: Electrons emitted from the cathode C are pulsed by the potentials applied to the control grid Gl by the oscillator 3. Thus groups or pulses of electrons are started toward the target. The accelerating voltage applied to the accelerating electrode G2 accelerates the groups of electrons as they enter the space between the velocity control electrodes G3 and G4. A potential of square wave form 2| is applied to the control electrodes G3 and G4. The effect of these potentials of square wave form is to compress the electron pulses and form the pulses into bunches of electrons, as indicated in Fig. 2. The compressed pulses or bunches approaching the phasing grid G5 and resonant cavity are admitted through the phasing grid G5 at the proper phase, which is determined by a phasing potential derived from the square Wave generator 9. The phasing potential 23 is preferably of the same square wave form and of the same frequency as the voltages applied to G3 and G4, although the phase is opposite and the voltages applied to G5 may be of greater amplitude.

In any event, the compressed electron bunches are so phased by the distance between G3 and G4 or the phase of the voltage on G5 that the bunches enter the space between G4 and G5 when it is field-free, and thus the compressed bunches are undistorted while in this space G4-G5. When the potential on G5 is positive, the bunches are further accelerated. The bunches give up energy to start and sustain oscillations within the resonant cavity. The frequency of the oscillations depends upon the number of electron density cycles or pulses per centimeter in each electron bunch and upon the electron bunch velocity. For example, f=nv, where f is the oscillation frequency, 'n is the number of pulses per centimeter in the bunch and o is the bunch velocity.

Thus, for a constant initial frequency f1, the output frequency f may be varied by changing the potential of G5. The form of the output wave will depend upon the decrement of circuit R. If the resonant circuit R is highly damped, the final output currents will be pulses of ultra high frequency energy; the output pulses are not to be confused with the input pulses. The output pulse length will depend upon the electron bunch transit time and the decrement of the circuit R. The output pulse frequency will be -that of the square wave generator. The carrier frequency of the output pulses is f. If the damping of the resonant cavity is low, a substantially continuous wave output may be obtained.

Thus, the compression or bunching of the electrons provides a means for multiplying the original frequency f1. High multiplication may be obtained by employing high compression in the space between G2 and G3 by applying potentials of large amplitude between G2 and G3, and by obtaining high acceleration in the space between G4 and G5 by applying potentials of large amplitude between G4 and G5.

The average number of cycles per second, of electron density, is unchanged, because the bunches are only grouped and compressed input pulses. Furthermore, the higher the compression frequency, the shorter will be the output Wave train. The system lends itself to amplitude or frequency modulation. The amplitude modulation is obtained by varying the potentials applied to Gl or G2,-which vary the average current.

Frequency modulation is obtained by varying the potential applied to G5.

A preferred embodiment of the invention is shown in Fig. 3 in which the elements are arranged as follows: An envelo-pe 3l houses a cathode 33; a control grid 35,; a hollow member 3l including a drift space 3E, a grid 4l, and a resonant cavity or resonant circuit portion 43; and a target electrode 115. The envelope is evacuated and is surrounded by a solenoid 37. The connections are as follows: The cathode and control grid are connected to a first oscillator de. The connection may include a biasing battery l. A second oscillator 53 is connected through a concentric line 55 to the grid 4I and the hollow member 3?. The hollow member is suitably biased with respect to ground by a battery 5l. The target electrode G5 is connected to the positive terminal of a battery 5S whose negative terminal is grounded.

Y The mode of operation is as follows: The electron beam 5I from the cathode is space charge modulated by the oscillatory potentials applied to the control grid 35. lI'he oscillatory potentials applied to` the second grid 4i impart velocity modulation to the beam. As the thus modulated ing a resonant circuit, said resonant circuit being tuned to a frequency which differs substantially from said predetermined frequency, and means for applying said grouped pulses to said circuit to establish oscillations therein of the frequency of said resonant circuit and of a frequency different from and independent of said predetermined frequency.

2. A frequency changer including means for creating an electron beam, means for varying the electron density of said beam to establish pulses of a predetermined fundamental frequency, means including an electrode -in the path of said beam, a source of modulating potentials which is so low in frequency compared to said fundamental frequency that there is no substantial change in voltage thereof during the passage of one of said pulses through the modulating spaces of said electrode, means for applying said potentials as potentials directly to said electrode, means including said electrode forming a drift space and a producing eld varying at said lower frequency for grouping said pulses into bunches, a resonant cavity, said resonant cavity being tuned to a frequency which differs substantially from said predetermined frequency, and means for directing said grouped pulses through said cavity to establish therein resonant oscillations of the frequency of said resonant cavity and of a frequency higher than said predetermined frequency and independent of said lower frequency.

3. A frequency changer including means for creating an electron beam, means for varying the electron density of said beam to establish pulses of a predetermined fundamental frequency,

means including an electrode in the path of said beam passes through the drift space 39, the faster electron pulses tend to gain on the slower ones. This establishes alternately, along the beam, regions of compressed pulses and regions of rareed pulses. The resonant cavity f3V is tuned to a frequency corresponding to that of the compressed or bunched pulses. The bunches establish resonant waves` in the cavity from .which outputqcurrents may be derived. If the voltages applied to the second grid 4l are of saw-tooth forni, the efficiency of the device will be increased since the spacing of the pulses in the regions of compression will be more uniform, and will contain. a higher percentage of the desired frequency,

I Claim as my invention:

1. A frequency changer including means for creating an electron beam, means for modulating saidY beam to obtain pulses of a predetermined fundamental frequency, means including an electrode in the path of said beam, a source of modulating potentials which is so 10W in frequency compared to said fundamental frequency that there is no substantial change in voltage thereof during the passage of one of said pulses through the modulating spaces of said electrode, means for applying said potentials as potentials directlyV to said electrode for grouping said pulses to vary said fundamental frequency, means includbeam, a source of modulatingpotentials which is so low in frequency compared to said fundamental frequency` that there is no substantial change in voltage thereof during the passage of one of said pulses through the modulating spaces of said electrode, means for applying said potentials as potentials directly to 'said electrode, means in- Cludne Said electrode forming 'a drift. spacerfor grouping said pulses into bunches, a resonantV resonant cavity for deriving oscillatory currents, y

electron density of s aid beam to form pulses of predetermined fundamental frequency, means including an electrodeiin the path of said beam, means including a source of modulating'potentials which is so vlovv in frequency compared to said fundamental frequency that there is no substantial change in voltage thereof during the passage of one of said pulses through the modulating spaces o f said electrode, means for applying said potentials as potentials directly to said electrode for compressing Said pulses into bunches, resonant cavity means, Y said resonant cavity means being tuned to a frequency. which differs substantially fromV said predetermined frequency, means for acceleratingv said bunches, means for creating an electromagnetic. eldj for admitting' said accelerated bunchesv into saidA cavity at a predetermined phase of the-field within said cavity to create oscillations therein of the frequency of said resonont cavity and of a frequency higher than and independent of said predetermined frequency.

5. A frequency changer including means for creating an electron beam, means for directing v said beam towards a target, means for establishing pulses of varying electron density in' said beam, means including an electrode in the path of Asaid beam, a source of modulating potentials which is so low in frequency compared to said es-V tablished frequency that there is no substantial change in voltage thereof during the passage of one of said pulses through the modulating spaces of said electrode, means for applying said potentials as potentials directly to said electrode for bunching said pulses, means for accelerating said hunched pulses, means intermediate said beam creating means and said target including a cavity having a resonant frequency higher than and independent of said initial pulse frequency, means including a biased electrode for phasing said bunches before admitting said bunches into said cavity at a predetermined ph'ase of the eld within vsaid cavity, and an output circuit for deriving from said cavity oscillations-of the frequency of said resonant cavity and of a frequency higher than an independent of said pulse frequency.

6, A frequency changer including means for creating an electron beam, means for directing said beam towards a target, means for establishing pulses of varying electron density iny said beam, means including an electrode in the path of said beam, a source of modulating potentials which is so low in frequency compared to said established frequency that there is no substantial ch'ange in voltage thereof during the passage of one of said pulses through the modulating spaces of said electrode, means for applying said potentials as potentials directly to said electrode for bunching said pulses, means for accelerating said hunched pulses, means intermediate said beam creating means and said target including a cavity having a resonant frequency 1w which is higher than and independent of said initial pulse frequency, means including means for producing an electromagnetic field for phasing said bunches before admitting said bunches into said cavity, and an output circuit for deriving from said cavity oscillations of a frequency ,f -nv Where j is in cycles per second, n is the number of pulses per centimeter in one of said bunches, and 'U is the bunch velocity in centimeters per second.

7. A frequency changer including a source of oscillations of an initial frequency, means for creating an electron beam, means including said source of oscillations for modulating said beam to form pulses, means including an electrode in the path of said beam, a source of'modulating potentials which is so low in frequency compared to said initial frequency th'at there is no substantial ch'ange in voltage thereof during the passage of one of said pulses through the modulating spaces of said electrode, means for applying said potentials as potentials directly to said electrode for bunching the pulses of said modulated beam, a resonator, said resonator being tuned to a frequency which differs substantially from said predetermined frequency, means for applying said hunched pulses to said resonator to obtain oscillations of the frequency of said resonator and of a frequency dependent upon the distance traveled by said bunches and their velo-cities and independent of said initial frequency, and means for applying said oscillations to a load circuit.

8. A frequency changer including a source of oscillations of an initial frequency, a source of electrons, means for forming saidv electrons into a beam, means including said source of oscillations for forming said beam into pulses, means including an electrode in the path' of said' beam, a source of modulating potentials which is so low in frequency comparedv to said initial frequency that there is no substantial change vin voltage thereof during the passage of one of said pulses through the modulating spaces of said electrode, means for applying said potentials as potentials directly to said electrode for bunching said pulses, means including a resonant cavity, said resonant cavityr being tuned to a frequency which differs substantially from said predetermined frequency, means for applying said bunched pulsesito said resonant cavity to establish oscillations of the frequency of said resonant cavity and of a frequency dependent upon the distance traveled by said bunches and their velocities land independent of said initial frequency.

9. A frequency changer including a source of initial oscillations, means for establishing an electron beam, means for applying said initial oscllations to said beam to form pulses, means including an electrode in the path of said beam, a source of modulating potentials which is so low in frequency compared to said initial frequency that there is no substantial change in voltage thereof during the passage of one of said pulses through the modulating spaces of said electrode, means for applying said potentials as potentials directly to said electrode for compressing said pulses, a resonant cavity, said resonant cavity being tunedvtc a frequency which differs substan-- tially from said initial frequency, and means including said cavity for deriving from said compressedv pulses oscillations of the resonant frequency and of a frequency dependent upon the distance traveled by said bunches and their velocities and independent of said initial oscillations.

10. A frequency multiplier including a source of initial oscillations, means for establishing an electron beam, means for applying said initial oscillations to said beam to form pulses, means including an electrode in the path of said beam, a source of modulating potentials which is so low in frequency compared to said initial frequency that there is no substantial change in voltage thereof during the passage of one of said pulses through the modulating spaces of said electrode, means for applying said potentials as potentials directly to said electrode for velocity modulating said pulses, means including said electrode forming a drift space for bunching said velocity-modulated pulses, means including a resonant cavity, said resonant cavity being tuned to a frequency which differs substantially from said initial frequency, and means for directing said hunched pulses through said cavity to establish oscillations of the frequency of said resonant cavity and of a frequency dependent upon the distance traveled by said bunches and their velocities and independent of said initial oscillations.

11. The method of generating ultra high frequency oscillations which includes creating an electron beam, modulating said beam to obtain pulses of electrons, compressing at a substantially lower frequency said pulses into similar bunches, directing said bunches along a predetermined path and deriving from said bunches an oscillatory current of a frequency dependent upon the distance traveled by said bunches, the velocity of said bunches and the number of pulses per centimeter in each bunch and independent of the modulating frequency.

12. The vmethod of generating ultra high frequency oscillations which includes creating an electron beam, modulating such beam to obtain pulses of electrons, velocity-modulating Yat a substantially lower frequency said pulses to form similar bunches of pulses, directing said bunches along a predetermined path, and deriving from said bunches oscillatory currents of a frequency dependent upon the distance traveled by said bunches along said path and their velocities and the number of pulses per centimeter in each bunch, and independent of the modulating frequency. Y Y

13. A frequency changer including means for creating an electron beam, means for modulating said beam to obtain pulses of a predetermined fundamental frequency, means including an electrode in the path of said beam, a source of modulating potentials which is so low in frequency compared to said fundamental frequency that there is no substantial change in voltage thereof during the passage of one of said pulses through the modulating spaces of said electrode, means for applying said potentials as potentials directly to said electrode for compressing said pulses into bunches, means including an oscillatory circuit, said oscillatory circuit being tuned to a frequency which diifers substantially from said predetermined frequency, means for applying bunches to said circuit to establish oscillations therein of the frequency of Said oscillatory circuit and of a frequency dependent upon the distance traveled by said bunches and their velocities and independent of said predetermined frequency, and means for varying the average velocity of said beam to vary the frequency of oscillations in said circuit.

said

14. The method of generating ultra high fre;

quency oscillations which includes creatingan electron beam, modulating said beam to obtain pulses of electrons, periodically and at a substantially lower frequency accumulating said pulses, periodically and at a substantiallyV lower frequency accelerating said accumulation to form similar bunches, directing said bunches along a predetermined path, and deriving from said bunches oscillatory currents of a frequency dependent upon the distance traveled by ysaid bunches, the velocity of said bunches and the number of pulses per centimeter in each bunch and independent of the modulating frequency.

15. A frequency changer including means for creating an electron beam,'means for modulating said beam to obtain pulses of a predetermined fundamental frequency, means including an electrodein the path of said beam, a source of modulating potential which is so low in frequency compared to said fundamental frequency that there is no substantial change in voltage thereof during the passage of one of said pulses through the modulating spaces of said electrode, means'for applying said potentials as potentials directly to said electrode for compressing said pulses into bunches, means including an oscillatory circuit, said oscillatory circuit being tun-ed to a frequency which differs substantially from said predetermined frequency, means for applying said bunches to said circuit to establish oscillations therein of the frequency of said oscillatory circuit and of a frequency dependent upon the distance traveled by said bunches and their velocities and independent of said predetermined frequency, and means for varying the amplitude of said oscillations in said circuit including means for varying the potential of said beam modulating means.

ERNEST G. LINDER. 

